Sewage treatment plants treat wastewater so that it can be safely released back into the environment. They use several stages to separate and break down organic waste and improve the water's quality. This article explains how sewage treatment plants work, what each part does and the different treatment processes that may be used.
What Is a Sewage Treatment Plant?
A sewage treatment plant is designed to treat the wastewater from your toilets, sinks, showers and other facilities before releasing it back into the environment. The plant separates solid waste from the wastewater and uses biological treatment methods to break down harmful organic matter.
Many systems use oxygen to support naturally occurring bacteria, which feed on the waste and help clean the water. The treatment process usually occurs in several stages: the solid material settles first, then the wastewater passes through a biological treatment process; a final settlement stage removes smaller particles before the treated water is discharged. The remaining sludge builds up inside the system and must be removed at suitable intervals.
What Happens During the Primary Treatment Stage?
During the primary treatment stage, wastewater enters the first chamber of the sewage treatment plant (the settlement chamber), and the heavier solid waste is separated from the liquid. As the wastewater stays in the chamber, heavier solids sink to the bottom and form sludge, whereas lighter materials, like fats, oils and grease, rise towards the surface. After this, the partly separated wastewater moves on to the next treatment stage.
The primary treatment stage helps reduce the amount of solid material that reaches the biological treatment area. This is important because too much solid waste can interfere with later treatment stages and reduce how effectively the plant works. The sludge that collects at the bottom of the chamber stays there until it is removed during routine emptying.
Primary treatment does not clean the wastewater. Instead, it prepares the liquid for further treatment.
What Is the Role of the Aeration Chamber?
The aeration chamber is an important part of many sewage treatment plants because it helps break down organic waste in the wastewater. After the primary treatment stage, the partly treated wastewater enters this chamber for further treatment.
Air is pumped into the chamber through an aeration system, which adds oxygen to the wastewater and supports naturally occurring aerobic bacteria. These bacteria feed on organic matter within the sewage and help break it down into simpler substances.
Keeping enough oxygen in the chamber is important because the bacteria need it to remain active. If aeration is reduced or stops, the biological treatment process can become less effective, which can lead to poor quality treated water and unpleasant smells.
The aeration chamber also keeps the wastewater moving, which helps the bacteria remain in contact with the waste they are treating. After this stage, the wastewater normally passes to a final settlement area where the remaining solids can separate from the treated liquid before being discharged.
How Does the Biological Treatment Process Work?
The biological treatment process uses naturally occurring microorganisms to break down organic waste in the wastewater. After the larger solids have been separated during the settlement stage, the remaining wastewater moves into an area where biological treatment takes place. In many sewage treatment plants, air is added to the wastewater to provide oxygen, which supports aerobic bacteria that feed on organic matter such as human waste and other biodegradable materials.
As the bacteria break down this material, the amount of pollution in the wastewater is reduced. The treated wastewater then moves to another settlement stage, where any remaining solid particles and biological material can settle out before the water is discharged. Biological treatment is important because it improves the quality of the wastewater before it returns to the environment. Without effective biological treatment, the discharged wastewater may contain much higher levels of organic pollution and harmful microorganisms.
How Do Air Pumps and Diffusers Help Treat Sewage?
Air pumps and diffusers help treat sewage by supplying oxygen to the wastewater inside the treatment plant. The air pump pushes air through the pipes to the diffusers, which release small bubbles into the treatment chamber. This oxygen supports aerobic bacteria that break down the organic waste in the sewage. The bubbles also help keep the wastewater moving, allowing the bacteria to stay in contact with the waste they need to treat.
This process is important because the bacteria need enough oxygen to work effectively. If the air pump or diffusers become blocked, damaged or stop working, the oxygen levels can fall, which can slow down the biological treatment process and reduce the quality of the treated wastewater.
What Happens in the Final Settlement Tank?
In the final settlement tank, the treated wastewater is fully separated from the remaining solid material before it leaves the sewage treatment plant. After the biological treatment process, the water may still contain small particles and biological matter.
Inside the final settlement tank, the water flow slows down, allowing the heavier particles to sink to the bottom. The clearer water remains at the top of the tank and can then move towards the outlet, ready to be discharged.
In some treatment plants, part of the settled sludge is returned to an earlier treatment stage, which helps maintain the microorganisms needed for biological treatment. The final settlement stage is important because it improves the quality of the treated wastewater before it's discharged.
How Is Treated Wastewater Discharged?
After the wastewater has passed through all the treatment stages, it is released from the sewage treatment plant through an outlet. In the UK, the discharge method your plant uses depends on the location of your property, the design of the system and any environmental rules that you must comply with.
The treated wastewater can be discharged into a suitable body of water, such as a stream or river. However, in some cases, it may be discharged into the ground through a drainage field or another suitable infiltration system. Before it's discharged, the treatment plant must remove enough waste and pollution for the water to meet the required standards. The sewage system must also be maintained properly so that it continues to treat the sewage effectively.
Why Do Bacteria Help Break Down Sewage?
Bacteria play an important role in sewage treatment because they help break down the organic waste in the wastewater. Sewage contains biodegradable material from your toilets, sinks and other sources, and naturally occurring bacteria feed on this material and convert it into simpler substances.
In many sewage treatment plants, aerobic bacteria are used during the biological treatment stage. These bacteria need oxygen to remain active, so air is usually pumped into the treatment chamber to help the bacteria grow and break down the organic matter more effectively. As the bacteria consume the waste, the amount of organic pollution in the wastewater is reduced.
The treated water can then move to a settlement stage, where any remaining solids and biological material are separated. This process is important because it improves the quality of the wastewater before it's discharged. Without active bacteria, the organic waste would not be treated as effectively, which can increase the risk of pollution.
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